The present invention relates to the production of biopolymers and more especially to the preparation of polysaccharides by fermentation using methanol as the sole source of assimilable carbon. The invention also relates to the use of these biopolymers as drag reducing agents, as thickening agents, emulsifiers, soil suspending agents, flocculants or deflocculants, etc.
Biopolymers have recently been the subject of increased research studies because of the interesting properties exhibited by such polymers and the various applications suggested by these properties. The polysaccharides which have been studied most are those produced by fermentation utilizing bacteria of the genus Xanthomonas which generally utilize carbohydrates as the source of assimilable carbon in a culture medium. These biopolymers act as versatile thickening agents for aqueous acids, alkalis and brines, and are good suspending agents for solids-in-water and oil-in-water dispersions, and act also as excellent rheology control agents. Thus, the xanthan gums find application in oil well drilling mud systems, as additives for secondary recovery of petroleum by water flooding, and as stabilizers, emulsifiers and thickeners in food products.
In view of economic considerations, however, it would be more desirable to employ petrochemicals as the source of assimilable carbon in fermentation systems rather than carbohydrates. Of petrochemicals, methane or methanol would be the most economical. Some studies have been made on bacteria utilizing these compounds as a carbon source. For example, Leadbetter and Foster (Archiv fur Mikrobiologie, 30, 91-118, 1958) isolated and grew several cultures of pseudomonads in a mineral salts medium with methane as the sole source of carbon and energy. Harrington and Kallio (Can. J. Microbiol., 6, 1-7, 1960) have published work on the oxidation of methanol by Pseudomonas methanica. But despite the numerous studies on the specific activities of methane- and methanol-utilizing bacteria and theorization as to the metabolic pathways, very little work has been conducted regarding characterization of the biopolymers formed or in investigating the properties and utilities of these products resulting from fermentation in culture media containing methane or methanol.
One factor prompting investigation of the properties of the biopolymers according to the present invention is that inexpensive conventional polymeric materials utilized in dilute aqueous solutions to produce a drag-reducing effect, such as polyethylene oxides and polyacrylamides, suffer from certain drawbacks. For example, these polymers are relatively unstable to salt and acid or alkaline conditions, and they tend to breakdown in molecular weight during flow as a result of turbulent conditions and moderate shearing forces. These disadvantageous factors are also present in many of the polymeric thickening agents presently being employed in drilling muds and flooding agents for secondary recovery of oil in the petroleum industry.